SUMMARY Atrial fibrillation (AF) is the most common cardiac arrhythmia of clinical significance, and it often results in devastating outcomes. Because current treatment is frequently ineffective, there is a critical need for an improved understanding of the mechanisms causing AF and novel strategies to treat it. Abundant evidence has linked oxidative stress to the pathogenesis and progression of AF, yet upstream therapy to target these processes has been ineffective. Lipid aldehydes are a major component of oxidative stress-related injury, and the most reactive products generated, isolevuglandins (IsoLGs), react almost instantaneously with proteins to cause dysfunction. Dicarbonyl scavengers have been developed that preemptively bind IsoLGs before they can interact with biologic targets. Using these tools, IsoLGs were recently identified as critical mediators in angiotensin II-mediated hypertension and Alzheimer's disease. Diseases of oxidative stress are also linked to proteotoxicity, or cellular dysfunction caused by misfolded proteins. In amyloid diseases like Alzheimer's, preamyloid oligomers (PAOs) are now recognized to be the primary cytotoxic species that correlates with disease progression. Notably, IsoLGs markedly accelerate PAO formation for amyloidogenic proteins. Based on our preliminary data, the goal of this proposal is to test the hypotheses that both IsoLGs and PAOs are biologically-relevant mediators that promote AF susceptibility, making them potential therapeutic targets. We have acquired compelling preliminary data to support the concept that IsoLGs and PAOs are drivers of the AF substrate: PAOs are commonly detected in human atrium, with the fibrillogenic protein atrial natriuretic peptide (ANP) a major component, and they associate with hypertension; IsoLGs and PAOs are formed in cellular and in vivo models associated with AF susceptibility, including rapidly-stimulated atrial cells, hypertension, obesity, and familial AF; and there is a beneficial effect of scavenging IsoLGs to reduce atrial PAO and AF burden. Moreover, a mutant form of ANP linked to familial AF markedly enhances the formation of cytotoxic ANP oligomers, and these PAOs accumulate in the atria of mice modeling the human disease. The first Aim will test the hypothesis that in hypertension and obesity, oxidative stress-mediated IsoLGs promote atrial cell injury and AF susceptibility. Aim 2 will test the hypothesis that mutant ANP oligomers alter atrial myocyte homeostasis to generate AF susceptibility, and they promote oxidative stress/IsoLG formation that can feed-forward to perpetuate the pathologic process. Finally, Aim 3 will test the hypothesis that in addition to hypertension, other AF risk factors linked to oxidative stress are also associated with accumulation of IsoLGs and/or cytotoxic PAOs, supporting their role in human disease. The proposed studies have major significance, given that IsoLG and PAOs may provide not only common mechanistic links between oxidative stress, proteotoxicity, common clinical risk factors, and AF, but also novel therapeutic targets in the prevention and/or treatment of this common arrhythmia.